Low-complexity optical force sensor for a medical device

ABSTRACT

An apparatus for detecting deformation of an elongate body may comprise a light source configured to sequentially provide light of multiple frequencies, an optical receiver configured to receive light from the light source, and a filter disposed between the light source and the optical detector. The filter may comprise multiple segments, each of the segments configured to filter light at one of the frequencies so as to alter the amount of light incident on said optical receiver. A total amount of light detected by the optical receiver may change during the sequence so as to be indicative of deformation of the elongate body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 13/753,400, filed 29 Jan. 2013, which is hereby incorporated byreference as though fully set forth herein.

BACKGROUND

a. Technical Field

The instant disclosure relates to elongate medical devices, such ascatheters and introducers, for example. More specifically, the instantdisclosure relates to the detection and measurement of external forceson an elongate medical device.

b. Background Art

Catheters are used for an ever-growing number of procedures, includingdiagnostic and therapeutic procedures. Such procedures involvenavigating the catheter through the patient's vasculature to abiological site and, for some procedures and some catheters, initiatingand/or maintaining contact between the tip of the catheter and tissue.During such navigation and procedures, it may be desirable to assess thedeformation of the catheter tip and/or the force applied to the tip ofthe catheter to determine if there is contact between the catheter tipand tissue and to ensure that the amount of force does not become sogreat that the catheter tip inadvertently damages the tissue, such as bypuncturing the tissue.

Many systems and methods are known for assessing the force on a cathetertip. However, known systems generally either involve multiple sensors(and thus may be more complicated or larger than desired) or do notdetect force with sufficient degrees of freedom (for example, magnitudeand/or direction of deflection and/or twisting).

The foregoing discussion is intended only to illustrate the presentfield and should not be taken as a disavowal of claim scope.

BRIEF SUMMARY

An embodiment of an apparatus for detecting deformation of an elongatebody may comprise a light source configured to provide light of multiplefrequencies and/or frequency bands, an optical receiver configured toreceive light from the light source, and a filter disposed between thelight source and the optical receiver. The filter may comprise multiplesegments, each of the segments configured to filter light at one of thefrequencies so as to alter the amount of light incident on the opticalreceiver. A total amount of light detected by the optical receiver maybe indicative of deformation of the elongate body.

An embodiment of an elongate medical device may comprise an elongateshaft having a distal end portion and a light source configured toprovide light of multiple frequencies and/or frequency bands along anoptical path, the optical path disposed within the distal end portion ofthe elongate shaft. The elongate medical device may further comprise anoptical receiver configured to receive light projected along the opticalpath and a filter disposed in the optical path. The filter may comprisemultiple segments, each of the segments configured to filter light atone of the frequencies and/or frequency bands so as to reduce the amountof light incident on the optical receiver.

A system for assessing force on a medical device may comprise anelectronic control unit (ECU) configured to receive a signal generatedby an optical receiver responsive to multiple frequencies of light, themultiple frequencies and/or frequency bands of light received by theoptical receiver in a predetermined sequence, and process the signal inaccordance with the predetermined sequence to determine an externalforce applied to the medical device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an elongate medical device.

FIG. 2 is a diagrammatic view of an embodiment of an optical forcesensor that may be used with the elongate medical device of FIG. 1.

FIG. 3 is a diagrammatic view of an optical filter of the optical forcesensor of FIG. 2 with a light beam projection incident thereon.

FIG. 4 is a diagrammatic view of the optical filter of FIG. 3, with theincident light beam projection shifted on the optical filter.

FIG. 5 is a diagrammatic view of the optical filter of FIG. 3, with theincident light beam projection rotated on the optical filter.

FIG. 6 is a schematic view of a system that may be used for determiningdeformation characteristics and external forces on the elongate medicaldevice of FIG. 1 using an optical force sensor.

FIG. 7 is a diagrammatic view of another embodiment of an optical forcesensor that may be used with the elongate medical device of FIG. 1.

FIG. 8 is a diagrammatic view of another embodiment of an optical forcesensor that may be used with the elongate medical device of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

Various embodiments are described herein with respect to variousapparatuses, systems, and/or methods. Numerous specific details are setforth to provide a thorough understanding of the overall structure,function, manufacture, and use of the embodiments as described in thespecification and illustrated in the accompanying drawings. It will beunderstood by those skilled in the art, however, that the embodimentsmay be practiced without such specific details. In other instances,well-known operations, components, and elements have not been describedin detail so as not to obscure the embodiments described in thespecification. Those of ordinary skill in the art will understand thatthe embodiments described and illustrated herein are non-limitingexamples, and thus it can be appreciated that the specific structuraland functional details disclosed herein may be representative and do notnecessarily limit the scope of the embodiments, the scope of which isdefined solely by the appended claims.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” or “an embodiment”, or the like, meansthat a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment.Thus, appearances of the phrases “in various embodiments,” “in someembodiments,” “in one embodiment,” or “in an embodiment”, or the like,in places throughout the specification are not necessarily all referringto the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments. Thus, the particular features, structures, orcharacteristics illustrated or described in connection with oneembodiment may be combined, in whole or in part, with the featuresstructures, or characteristics of one or more other embodiments withoutlimitation given that such combination is not illogical ornon-functional.

It will be appreciated that the terms “proximal” and “distal” may beused throughout the specification with reference to a clinicianmanipulating one end of an instrument used to treat a patient. The term“proximal” refers to the portion of the instrument closest to theclinician and the term “distal” refers to the portion located furthestfrom the clinician. It will be further appreciated that for concisenessand clarity, spatial terms such as “vertical,” “horizontal,” “up,” and“down” may be used herein with respect to the illustrated embodiments.However, surgical instruments may be used in many orientations andpositions, and these terms are not intended to be limiting and absolute.

Referring now to the Figures, in which like reference numerals refer tothe same or similar features in the various views, FIG. 1 is anisometric view of an embodiment of an elongate medical device 10 thatmay include a low-complexity optical force sensor. The elongate medicaldevice 10 may comprise, for example, a diagnostic and/or therapydelivery catheter, an introducer or sheath, or other like devices. Forpurposes of illustration and clarity, the description below will be withrespect to an embodiment wherein the device 10 comprises a catheter(i.e., catheter 10). It will be appreciated, however, that embodimentswherein the device 10 comprises elongate medical devices other than acatheter remain within the spirit and scope of the present disclosure.

The catheter 10 may comprise a shaft 12 having a distal end portion 14and a proximal end portion 16. The catheter 10 may be configured to beguided through and disposed in the body of a patient. Accordingly, theproximal end portion 16 may be coupled to a handle 18, which may includefeatures to enable a physician to guide the distal end portion 14 toperform a diagnostic or therapeutic procedure such as, for example only,an ablation procedure on the heart of the patient. Accordingly, thehandle 18 may include one or more manual manipulation mechanisms suchas, for example, rotational mechanisms and/or longitudinal mechanisms,coupled to pull wires for deflecting the distal end portion 14 of theshaft 12. Exemplary embodiments of manipulation mechanisms, pull wires,and related hardware can be found, for example only, in U.S. patentapplication publication no. 2012/0203169, hereby incorporated byreference in its entirety. The handle 18 may further include one or moreelectromechanical connectors for coupling to a mapping and navigationsystem, an ablation generator, and/or other external systems. Forexample, an electromechanical connector may provide a connection betweenan optical force sensor disposed in the catheter 10 and an externalelectronic control unit (see FIG. 6). The handle 18 may also include oneor more fluid connectors for coupling to a source and/or destination offluids such as, for example only, a gravity feed or fixed orvariable-rate pump.

The distal end portion 14 of the shaft 12 may include a number ofelectrodes 20, 22 for applying ablation energy to tissue, acquiringelectrophysiology data from tissue, determining the position andorientation (P&O) of the shaft 12, and/or other purposes known in theart. In an embodiment, the electrode 20 may be a distal tip electrode 20disposed on a distal tip 24 of the shaft 12, and the electrodes 22 maybe ring electrodes 22. The electrodes 20, 22 may be coupled toelectrical wiring within the shaft 12, which may extend to the handle 18and to electromechanical connectors for coupling to external systems, asdescribed above.

The distal end portion 14 may also include one or more fluid ports ormanifolds for distributing or collecting fluids such as, for exampleonly, irrigation fluid during an ablation procedure. The fluid ports maybe fluidly coupled with one or more fluid lumens extending through theshaft 12 to the handle 18 and a fluid connector for coupling to externalfluid sources and/or destinations, as described above. One or morelumens may also be provided through the shaft 12 for passing a secondelongate medical device therethrough. In some embodiments, for example,the elongate medical device 10 comprises an introducer that includes atleast one lumen configured to receive another device such as a catheteror probe.

The shaft 12 may also include a number of other features, such as one ormore electromagnetic sensors for position and navigation, temperaturesensors, and other sensors known in the art. One such sensor type thatmay be included may be for detecting the contact force between thedistal tip 24 and tissue. The contact force may be assessed, forexample, to ensure that the distal end portion 14 does not applyexcessive force to tissue so as to inadvertently puncture or otherwisedamage the tissue, to determine if contact is sufficient for an ablationprocedure, and/or other purposes known in the art. In an embodiment, thedistal end portion 14 may include an optical force sensor, as will bedescribed in conjunction with FIGS. 2-8.

FIG. 2 is a diagrammatic view of an embodiment of an optical forcesensor 26. The force sensor 26 may include a light source 28, an opticalfilter 30, and an optical receiver 32. The light source may projectlight along an optical path 34 towards the filter 30 and receiver 32.Referring to FIGS. 1 and 2, the force sensor 26 may be disposed in anelongate medical device, such as the catheter 10, for determining thedeflection characteristics of the catheter 10 and, in turn, the externalforce applied to the catheter 10.

The force sensor 26 (i.e., the light source 28, optical filter 30, andoptical receiver 32) may be secured within the shaft 12 or other deviceusing techniques known in the art. In an embodiment, the force sensor 26may be disposed in the distal end portion 14 of the shaft 12. Forexample, the force sensor 26 (i.e., one or more of the light source 28,the filter 30, and the optical receiver 32) may be placed within about0.5 inches to about 2 inches of the distal tip 24. In an embodiment, theforce sensor 26 may be secured within the shaft 12 such that the lightsource 28, optical filter 30, optical receiver 32, and optical path 34are insulated or sealed from fluid.

The light source 28 may include, in an embodiment, a light sourceconfigured to output light of multiple different frequencies. Forexample, the light source 28 may include a multi-color light-emittingdiode (LED)—i.e., a single apparatus having multiple LEDs, each capableof emitting light of a particular frequency and/or frequency band, asknown in the art. In an embodiment, the light source 28 may include amulti-color LED configured to output three or four colors of light, suchas red, blue, green, and yellow. A multi-color LED configured to outputfewer, more, and/or different colors may be used in addition oralternatively, in an embodiment.

In an embodiment, a multi-color LED may be chosen for the light source28 because it is “mechanically single”—i.e., a single die, package, chipor apparatus—yet capable of outputting multiple frequencies of light, asdescribed above. In an embodiment, a mechanically-single light source 28other than a multi-color LED may be included in the light source 28.Light from the light source 28 may be output in a beam having asubstantially circular, elliptical, square, rectangular, or other shape.For reasons that will be explained below, it may be advantageous, in anembodiment, for the light source 28 to output a non-circular projectionon the filter 30 such as an elliptical or rectangular shape.

Although the light source 28 will be described with reference to amulti-color LED, other light sources may be used. Furthermore, althoughdifferent “colors” of light will be described, it should be understoodthat “color” is merely used as a proxy herein for a particular frequencyand/or frequency band of light. In an embodiment, one or morefrequencies of light output by the light source 28 may be in some partof the electromagnetic spectrum other than visible light. Furthermore,the light source 28 may be configured to output any number offrequencies and/or frequency bands of light.

The optical filter 30 may comprise a number of segments 36, 38, 40, 42,each configured to filter a particular color of light. For example, afirst filter segment 36 may be configured to filter blue light, a secondfilter segment 38 may be configured to filter green light, a thirdfilter segment 40 may be configured to filter yellow light, and a fourthfilter segment 42 may be configured to filter red light. Though eachfilter segment 36, 38, 40, 42 is described herein with reference tofiltering a particular color, it should be understood that, again, coloris merely used as a proxy for light frequency. Just as the light source28 may be configured to output one or more frequencies of light in thenon-visible portions of the spectrum, one or more of the filter segments36, 38, 40, 42 may be configured to filter light frequencies in thenon-visible portions of the spectrum.

Filter, as used herein, may be used to refer to passing or rejecting (ina relative sense, as explained below) a particular frequency or set offrequencies. In an embodiment, each segment 36, 38, 40, 42 of the filter30 may be configured to pass a single frequency of light and/orfrequency band of light and substantially reflect and/or absorb theremaining frequencies. In an embodiment, a particular filter segmentneed not be a perfect or ideal filter—i.e., it need not pass 100% of thedesired frequency while rejecting 100% of undesired frequencies.Instead, in an embodiment, it may be sufficient for each filter segment36, 38, 40, 42 to merely provide a substantial difference between theamount of a desired light at a particular frequency that is passed andthe amount of undesired light at other frequencies that is passed. In anembodiment, it may be sufficient, for example, for a filter segment 36,38, 40, 42 to pass 60% or more of light of a desired frequency orfrequency band and 40% or less of light of undesired frequencies orfrequency bands. Of course, more discerning filter segments 36, 38, 40,42 may be used, in an embodiment. For example, in an embodiment, one ormore of the filter segments 36, 38, 40, 42 may pass about four times asmuch of a desired frequency and/or frequency band than of otherfrequencies produced by the source 28. In another embodiment, one ormore of the filter segments 36, 38, 40, 42 may pass about seven times asmuch of a desired frequency than of other frequencies and/or frequencybands.

Each filter segment 36, 38, 40, 42 may comprise a plastic or polymersheet, wafer, or other structure. The filter segments 36, 38, 40, 42 mayalso comprise glass or another material known in the art for lightfiltering, and may include one or more layers of one or more materials.Furthermore, the different segments 36, 38, 40, 42 may comprisedifferent materials, in an embodiment.

Though the filter 30 is illustrated and described in terms of anembodiment having four segments 36, 38, 40, 42, 44, more or fewer thanfour segments may be included in the filter 30. In an embodiment, thenumber of segments in the filter 30 may be equal to or greater than thenumber of colors of light output by the light source 28. Furthermore,although the segments 36, 38, 40, 42 are shown as occupying equalquadrants of the filter 30, alternative filter arrangements arepossible.

The optical receiver 32 may comprise a light detector configured togenerate an output signal according to the amount or intensity of lightimpinging on the receiver 32. In an embodiment, the receiver 32 may beroughly or approximately frequency-indifferent—i.e., substantiallyequally responsive to light of all frequencies and/or frequency bandsoutput by the light source 28. For example, the receiver 32 may beequally or approximately equally responsive to all frequencies of lightin the visible spectrum, in an embodiment.

The filter 30 and receiver 32 may be of substantially the same size andshape and may be oriented substantially perpendicular to the opticalpath 34, in an embodiment. As shown in FIG. 2, the filter 30 andreceiver 32 may be substantially circular. The filter 30 and receiver 32may have different shapes in other embodiments.

In operation, the light source 28 may provide light of multiplefrequencies along the optical path 34, which may be filtered by thesegments 36, 38, 40, 42 of the filter 30 and detected by the opticalreceiver 32. In an embodiment, different colors of light may betransmitted by the light source 28 in a predetermined sequence—i.e., afirst color for a first period of time, then a second color for a secondperiod of time, and so on. According to the deflection, twisting, and/orother deformation of the portion of the shaft 12 (or other device) inwhich the optical path 34 is disposed, the amount of light impinging ona given segment 36, 38, 40, 42 of the filter 30 may change. Because thedifferent segments 36, 38, 40, 42 may filter different colors, as theamount of light impinging on the segments 36, 38, 40, 42 changes as theshaft 12 deforms, the amount of light reaching the receiver 32 willchange as different colors of light are provided. Accordingly, byassessing the amount of light detected by the receiver 32 at any giventime, in conjunction with the knowledge of what color of light istransmitted by the light source at that time, the deflection, twisting,and/or other deformation characteristics of the portion of the shaft 12(or other device) in which the optical path 34 is disposed can bedetermined. Based on the deflection, twisting, and/or other deformation,the exterior force on the distal tip 24 can be determined. Themathematical operations behind these determinations will be describedmore fully below, following examples of shift and rotation of incidentlight on the filter 30 and receiver 32.

Compression and expansion of the optical path 34 (i.e., of the portionof the shaft 12 in which in the optical path 34 is disposed) can also bedetected by an embodiment the sensor 26. For example, an aperture orother structure may be placed between the light source 28 and thereceiver 32 such that compression or expansion of the shaft 12 (i.e., achange in the distance between the light source 28 and the receiver 32)results in a change in the total amount or intensity of light on allsegments 36, 38, 40, 42. By measuring this total change, compression orexpansion of the shaft 12 can be detected and quantified.

The neutral-state (i.e., undeformed state of the portion of the shaft 12in which the force sensor 26 is disposed) distance between the lightsource 28 and the receiver 32 and the relative orientations of the lightsource 28 and the receiver 32 may be determined according to the bendingcharacteristics of the shaft 12. In general, for reasons explainedbelow, an excess of bending of the portion of the shaft 12 in which thesensor 26 is disposed may reduce the effectiveness of the sensor 26.Accordingly, as the stiffness of the device in which the sensor 26 isdisposed increases (and thus the ability of a small section of thedevice to bend beyond the effective range of the sensor 26 decreases),the distance between the light source 28 and the receiver 32 may alsoincrease. In an embodiment, the light source 28 may be placed about 0.5inches to about 2 inches from the receiver 32.

FIGS. 3-5 are diagrammatic views of the filter 30 with incident light 44of a rectangular shape projected thereon from the light source 28. Asnoted above, the beam projection from the light source 28 may also besubstantially square, circular, elliptical, or in some other shape(e.g., asymmetric)—the incident light 44 may thus also be in some othershape. FIGS. 3-5 also show a center point 46 indicating the geometriccenter of the incident light 44, an X-axis, and a Y-axis, though itshould be understood that such labels are provided for explanatorypurposes only.

In FIG. 3, the incident light 44 is projected equally upon the foursegments 36, 38, 40, 42 of the filter 30 with the center point 46 of thebeam projection coincident with the origin O of the X-Y axis, indicatinga non-deflected state of the light source 28 relative to the filter 30(and thus a non-deflected state of the portion of the shaft 12 in whichthe sensor 26 is disposed). FIG. 4 illustrates the incident lightshifted along both the X and Y axes, with the center point 46 within thefirst filter segment 36, indicating a deflected state of the lightsource 28 relative to the filter 30. FIG. 4 may represent, for example,a situation in which the shaft 12 is slightly bent or displaced as aresult of contact of the device 10 with adjacent tissue, resulting in ashift in the center point 46 of the incident light projection 44 on thefilter 30. FIG. 5 illustrates the incident beam projection rotated aboutthe origin of the X-Y axis, indicating a rotated state of the lightsource 28 relative to the filter 30. FIG. 5 may represent, for example,a situation in which the shaft 12 is twisted, resulting in a concomitantrotation of the incident light beam projection 44 on the filter 30.

As the incident light shifts and/or rotates, the respective amounts oflight through the different filter segments 36, 38, 40, 42 change. Thesensor 28 takes advantage of this by projecting different colors oflight in a predetermined sequence, with each color corresponding to oneor more of the filter segments 36, 38, 40, 42. Accordingly, in adeflected or rotated state (such that the amount of incident light 44 isnot equal across all filter segments 36, 38, 40, 42), the amount oflight incident on the optical receiver 30 will change between differenttransmitted colors. Due to this change, the deflection and/or rotationof the light source 28 relative to the filter 30 and receiver 32 (andthus the deflection and/or rotation of the portion of the shaft 12 inwhich the sensor 26 is disposed) can be determined. Illustrativeexamples follow.

Example Deflection in Two Dimensions

An embodiment of the sensor 26 may be used to measure deformation withtwo degrees of freedom deflection of the shaft 12, and more specificallythe distal end portion 14, in two dimensions (i.e., along the X- andY-axes as shown in FIGS. 3-5). In such an embodiment, the light source28 may be configured to output two colors of light. For example, thelight source 28 may be a two-color LED configured to output blue lightand red light.

When the shaft 12 is in a non-deflected state, the light source 28projects rectangular incident light 44 onto the filter 30, with thecenter point 46 coincident with the center of the filter and origin ofthe arbitrarily-assigned X-Y coordinate system. In the rectangularcoordinates of FIGS. 3-5, the incident light 44 extends between (−A) andA in the X-direction and between (−B) and B in the Y-direction.

Let the intensity of light incident onto the filter be uniform acrossand throughout the incident light 44. The products of incident (onto thefilter 30) light intensity, filter segment 36, 38, 40, 42 transmissioncoefficient, and sensitivity per unit area of the receiver 32 can bedenoted as ν_(1R) and ν_(1B) for red and blue light, respectively,passing through the first filter segment 36, ν_(2R) and ν_(2B) for thesecond filter segment 38, ν_(3R) and ν_(3B) for the third filter segment40, and ν_(4R) and ν_(4B) for the fourth filter segment 42. As usedherein, the subscript R refers to red light, and the subscript B refersto blue light.

In an embodiment, the second filter segment 38 may preferably pass redlight (i.e., the second filter segment 38 may prefer, or pass, more redlight than another color or set of colors), the fourth filter segment 42may preferably pass blue light, and the first and third filter segments36, 40 may equally pass red and blue light. Of course, otherdistributions of filter segments 36, 38, 40, 42 may be used in anembodiment, and one of skill in the art could readily adapt theequations presented below to a different arrangement of filter segments36, 38, 40, 42.

The output of the optical receiver 32 for red light in a non-deflectedstate, V_(det) _(_) _(R0), may be defined as:

V _(det) _(_) _(R0) =AB(ν_(1R)+ν_(2R)+ν_(3R)+ν_(4R))  (1)

and the output of the optical receiver 32 for blue light in anon-deflected state, V_(det) _(_) _(B0) may be defined as:

V _(det) _(_) _(B0) =AB(ν_(1B)+ν_(2B)+ν_(3B)+ν_(4B))  (2)

where the subscript “0” indicates a neutral state throughout thisdisclosure—here, zero deflection.

To separately measure red and blue light detected by the opticalreceiver, red and blue light may be transmitted and detected in atime-multiplexed arrangement. The light source 28 may first output bluelight, and the output of the optical receiver 32 may be stored orprocessed as blue light output. The light source 28 may then output redlight, and the output of the optical receiver 32 may be stored orprocessed as red light output. The respective periods of time for whichred and blue light may be output may each be on the order ofmilliseconds, in an embodiment, though the application of the sensor 26is certainly not so limited. The respective periods of time may be thesame as each other, or may be different from each other.

As a result of deflection of the shaft 12, the incident light 44 maymaintain substantially the same shape and orientation, but may shift byΔx and Δy in the X- and Y-directions, respectively, as shown in FIG. 4.Given such a shift, the output of the receiver 32 for a single color maybe:

V _(det) _(_)_(i)=ν_(1i)(A+Δx)(B+Δy)+ν_(2i)(A−Δx)(B+Δy)+ν_(3i)(A−Δx)(B−Δy)+ν_(4i)(A−Δx)(B−Δy)  (3)

where i=R or B.

Assuming that Δx and Δy are much smaller than A and B, it can be assumedthat equation (3) above is linear (i.e., that the products of Δx and Δyin the various terms of equation (3) are negligible). In this regard, itshould be understood that the shift illustrated in FIG. 4 is exaggeratedfor clarity of illustration. Under such an assumption, and given V_(det)_(_) _(R0) and V_(det) _(_) _(B0), equation (3) may reduce to:

V _(det) _(_) _(i) =V _(det) _(_)_(i0)+(ν_(1i)−ν_(2i)−ν_(3i)+ν_(4i))(BΔx)+(ν_(1i)+ν_(2i)−ν_(3i)−ν_(4i))(AΔy)  (4)

where i=R or B, again. It should be noted that equation (4) may alsowork with an elliptical beam of incident light, rather than arectangular beam 44.

Equation (4) can be solved with high accuracy for Δx and Δy (i.e., amagnitude and direction thereof) if the values of the coefficient matrixof the right hand side of equation (4) do not differ by more than afactor of 3. That coefficient matrix, referred to below as ν_(mat1),characterizes the relationship between Δx, Δy, and V_(det) _(_) _(R),V_(det) _(_) _(B) and is shown in equation (5) below:

$\begin{matrix}{v_{{mat}\; 1} = \begin{bmatrix}v_{RX} & v_{RY} \\v_{BX} & v_{BY}\end{bmatrix}} & (5)\end{matrix}$

where ν_(RX)=ν_(1R)−ν_(2R)−ν_(3R)+ν_(4R),ν_(RY)=ν_(1R)+ν_(2R)−ν_(3R)+ν_(4R), ν_(BX)=ν_(1B)−ν_(2B)−ν_(3B)+ν_(4B),and ν_(BY)=ν_(1B)+ν_(2B)−ν_(3B)+ν_(4B). Thus, it should be noted that inν_(mat1), the subscript X to the X-direction shown in FIGS. 3-5.

Series of equations (4) will result in two equations (one for bluelight, one for red) and two unknowns (Δx and Δy). Accordingly, Δx and Δymay be determined according to known systems and methods for solving asystem of several equations with several unknowns.

Once Δx and Δy are determined, the deflection of the shaft 12 over theoptical path 44 may be determined. For small deformations (i.e., smalldegrees of deflection), the angles α, β of deflection in the X- andY-directions, respectively, are proportional to Δx and Δy, respectively.If the coefficient of proportionality between α and Δx is μ_(α) and thecoefficient of proportionality between β and Δy is μ_(β), then thecolumn vector with components (α, β) is given by the following matrixequation (6):

$\begin{matrix}{\begin{pmatrix}\frac{\alpha}{\mu_{\alpha}} \\\frac{\beta}{\mu_{\beta}}\end{pmatrix} = {{{inv}\left( v_{{mat}\; 1} \right)}\begin{pmatrix}{V_{\det_{—}R} - V_{\det_{—}R\; 0}} \\{V_{\det_{—}B} - V_{\det_{—}B\; 0}}\end{pmatrix}}} & (6)\end{matrix}$

where α and β are expressed in radians and inv represents matrixinversion.

The coefficients of proportionality μ_(α), μ_(β) may be determinedapproximately according to the design of the shaft 12, and may bedetermined more precisely through a calibration process. For example,one potential calibration procedure may include deflecting the shaft 12in a number of known deflections (i.e., with known α and β), measuringV_(det) _(_) _(R) and V_(det) _(_) _(B), and setting μ_(α) and μ_(β)using equation (6).

For simplicity of calculation and demonstration, the above equations(1)-(6) include assumptions that incident light 44 is coincident on thefilter 30 for both blue and red light, that the shape and size ofincident light 44 does not change with deflection of the shaft 12, andthat light intensity is uniform across and throughout the incident light44. In real applications, these assumptions do not need to hold.Instead, it may be necessary for only two assumptions to hold for thecalculation of α, β according to equations (1)-(6) to be accurate.First, deflection of the shaft 12 (i.e., of the light source 28 relativeto the filter 30) must be small enough for the linearity of equation (4)to apply. In an embodiment, this may include deflection of up to about15°. Second, the changes in output from the receiver 32 for blue lightand red light must not be linearly dependent.

From the deflection angles α, β, the exterior forces applied to thedistal tip 24 can be calculated. Under normal operating conditions ofthe catheter 10, deformations such as deflection, twist, and compressionare sufficiently small for linear elastostatics to apply. Elastostaticsis the study of linear elasticity under the conditions of equilibrium,in which all forces on an elastic body (i.e., the shaft 14) sum to zero,and the deformations are not a function of time.

Linear elasticity models materials as continua. The fundamental“linearizing” assumptions of linear elasticity are small deformations(or strains) and linear relationships between the components of stressand strain. The equilibrium equations of elastostatics that may be usedto calculate forces on the distal tip 24 according to calculateddeformation are given by equations (7)-(9) below. Equation (7) is thelinear elasticity equation of motion:

σ_(ji,j) =F _(i) =ρd _(tt) u _(i)  (7)

where σ_(ji) is the Cauchy stress tensor (i.e., a tensor matrix having irows and j columns), the j subscript stands for the partial derivativeover the j-th spatial coordinate, F_(i) is the i-th component of thelocal body force per unit volume, ρ is the local mass density, u_(i) isthe displacement component along the i-th spatial coordinate of arectilinear reference frame (the directions of which may, but do notneed to, coincide with directions corresponding to deflections α, β) andd_(tt) indicates

$\frac{^{2}}{t^{2}}.$

Equation (7) results in three independent equations with six unknowns.

Equation (8) is the linear elasticity strain-displacement equation:

$\begin{matrix}{ɛ_{i,j} = \frac{u_{j,i} + u_{i,j}}{2}} & (8)\end{matrix}$

where ε_(i,j) is the strain and u is again displacement. Equation (8)results in 6 independent equations with nine unknowns.

Equation (9) is the constitutive equation:

σ_(ij) =C _(ijkl)ε_(kl)  (9)

where C_(ijkl) is the stiffness tensor, which is based on the materialcharacteristics of the shaft. Once the Cauchy stress tensor σ_(ji) iscalculated, the force/torque surface density distribution over thecatheter surface is obtained therefrom. Equation (9) results in sixindependent equations with no additional unknowns.

Equations (7)-(9) give a series of fifteen equations with fifteenunknowns. Methods are known in the art for solving a series ofindependent equations with an equal number of unknowns. By applying oneor more of such known methods, the forces on the distal tip 24, or otherportion of the shaft 12 in which the sensor 26 is disposed, can becalculated.

Example Deflection in Two Dimensions and Twisting

An embodiment of the sensor 26 may be used to measure deformation withthree degrees of freedom—deflection of the shaft 12, and morespecifically the distal end portion 14, in two dimensions (i.e., alongthe X- and Y-axes as shown in FIGS. 3-5), as well as twisting about anaxis (i.e., rotation of the light source 28 relative to the filter 30about an axis that is perpendicular to the X-Y plane in FIGS. 3-5)(i.e., about the beam axis). Such an axis may be, in an embodiment, theaxis of the shaft 12. In such an embodiment, the light source 28 may beconfigured to output three colors of light, such as red, blue, andgreen.

As noted above, when the shaft 12 is in a non-deflected state, the lightsource 28 projects a rectangular incident light projection 44 onto thefilter 30, with the center point 46 coincident with the center of thefilter and origin O of the arbitrarily-assigned X-Y coordinate system(see FIG. 3). In the rectangular coordinates of FIGS. 3-5, the incidentlight 44 extends between (−A) and A in the X-direction and between (−B)and B in the Y-direction.

While deflection of the shaft 12 may shift the position of incidentlight 44 as shown in FIG. 4 and as discussed above, twisting of theshaft 12 may rotate the light source 28 relative to the filter 30, andthus rotate the incident light beam 44, as shown in FIG. 5. Let theangle of rotation be γ. Output of the receiver may be V_(det) _(_) _(B)for blue light, V_(det) _(_) _(R) for red light, and V_(det) _(_) _(G)for green light. Once again, the output of the receiver may begenerically referred to as V_(det) _(_) _(i), with i=R, G, B. Accordingto equations (1) and (2) above, and a third equation substantially thesame as equations (1) and (2) for green light, the zero-deflection,zero-twist outputs of the receiver V_(det) _(_) _(B0), V_(det) _(_)_(R0), V_(det) _(_) _(G0) may be determined. The effect of deflection onV_(det) _(_) _(i) in the X- and Y-directions may be accounted for byequation (4). An additional term may then be added to V_(det) _(_) _(i)to account for twist, as discussed below.

Referring to FIG. 5, let the four corners of the incident light 44 onthe first filter portion 36 be O (the origin), L (the point at which theincident light beam projection 44 crosses the X axis), I (the vertex ofthe incident light 44 in the first filter portion 36), and P (the pointat which the incident light 44 crosses the Y-axis). The portion of thefirst filter portion 36 that is bounded by these four points is referredto below as LIPO, and the area of that portion A_(LIPO). Further, let Mbe the point of the incident light beam projection 44 that crosses theX-axis in a neutral state (i.e., such that L₀=M), and let Q be the pointof the incident light beam projection that crosses the Y-axis in aneutral state (i.e., such that P₀=Q). The portion of the filter boundedby points O, M, Q, and I is referred to below and MIQO, and the area ofthat portion A_(MIQO). In a neutral state, A_(LIPO)=A_(MIQO). Thus,A_(LIPO) _(_) ₀=A_(MIQO). Still further, the triangle bounded by pointsO, P, and Q is referred to as QPO, and its area A_(QPO). The trianglebounded by points O, L, and M is referred to as MOL and its areaA_(MOL).

The difference between A_(LIPO) and A_(MIQO) (and thus, the differencein the light incident on the first filter portion 36 between a neutralstate and a twisted state) is a function of the areas of QPO and MOL asshown in equation (10) below:

A _(LIPO) −A _(MIQO) =A _(MOL) −A _(QPO)  (10)

The areas of QPO and MOL are, respectively, functions of the rotationangle γ, as shown in equations (11) and (12) below:

$\begin{matrix}{A_{MOL} = {\frac{\left| {OM} \middle| {}_{2}\mspace{14mu} {\tan (\gamma)} \right.}{2} = \frac{A^{2}\mspace{14mu} {\tan (\gamma)}}{2}}} & (11) \\{A_{QPO} = {\frac{\left| {OP} \middle| {}_{2}\mspace{14mu} {\tan (\gamma)} \right.}{2} = \frac{B^{2}\mspace{14mu} {\tan (\gamma)}}{2}}} & (12)\end{matrix}$

where OM and OP are the vectors between points O and M and O and P,respectively.

Accordingly, the difference between A_(LIPO) and A_(MIQO) is also afunction of the rotation angle γ, as shown by reducing equations(10)-(12) to equation (13) below:

$\begin{matrix}{{A_{LIPO} - A_{MIQO}} = \frac{\left( {A^{2} - B^{2}} \right){\tan (\gamma)}}{2}} & (13)\end{matrix}$

At angles of γ of much less than one radian, such as 0.2 radians orless, for example, tan(γ)≈γ, allowing equation (13) to be furtherreduced to equation (14) below, which may be computationally moreefficient:

$\begin{matrix}{{A_{LIPO} - A_{MIQO}} = \frac{\left( {A^{2} - B^{2}} \right)\gamma}{2}} & (14)\end{matrix}$

It should be noted that equation (14) (or its equivalent) would not workfor circular incident light because circular incident light does notchange across the filter segments 36, 38, 40, 42 as it rotates due totwist. Accordingly, in an embodiment, a rectangular or elliptical(non-circular) or another rotationally asymmetric beam projection shapefrom the light source 28 may be used to detect twist.

Equation (14) above is the contribution of twist to the differentialamount of light incident on the first filter portion. The same analysismay be performed for the second, third, and fourth filter portions.Accordingly, equation (14) may be added to equation (4) above (whichcontains the contributions of X-axis and Y-axis shifting to thedifferential amount of light incident on a given filter portion) toarrive at equation (15) below, which gives the total differential amountof light incident on the optical receiver for three degrees of freedom(i.e., X-axis shift, Y-axis shift, and twist):

$\begin{matrix}{V_{\det_{—}i} = {V_{\det_{—}i\; 0} + {\left( {v_{1\; i} - v_{2\; i} - v_{3\; i} + v_{4\; i}} \right)\left( {B\; \Delta \; x} \right)} + {\left( {v_{1\; i} + v_{2\; i} - v_{3\; i} - v_{4\; i}} \right)\left( {A\; \Delta \; y} \right)} + {\left( {v_{1\; i} - v_{2\; i} + v_{3\; i} - v_{4\; i}} \right)\frac{\left( {A^{2} - B^{2}} \right)}{2}\gamma}}} & (15)\end{matrix}$

As in the two degrees-of-freedom example, the angles α, β of deflectionin the X- and Y-directions, respectively, are proportional to Δx and Δy.Series of equations (15) will result in three equations (one for bluelight, one for red, and one for green) and three unknowns (Δx, Δy andγ). Accordingly, Δx, Δy, and γ (i.e., both the magnitude and directionthereof) may be determined according to known systems and methods forsolving a system of several equations with several unknowns.

Equation (15) can be solved with high accuracy for Δx, Δy, and γ if, inan embodiment, the singular values of the 3×3 coefficient matrix givenby the right-hand side of equation (15) do not differ by more than afactor of about 4. The coefficient matrix, referred to below as ν_(mat2)relates the values of BΔx, AΔy, and (A²−B²)γ to V_(det) _(_) _(R),V_(det) _(_) _(G) and V_(det) _(_) _(B), and is shown as matrix (16)below:

$\begin{matrix}{v_{{mat}\; 2} = \begin{bmatrix}v_{RX} & v_{RY} & v_{R\; \gamma} \\v_{BX} & v_{BY} & v_{B\; \gamma} \\v_{GX} & v_{GY} & v_{G\; \gamma}\end{bmatrix}} & (16)\end{matrix}$

where ν_(RX)=ν_(1R)−ν_(2R)−ν_(3R)+ν_(4R),ν_(RY)=ν_(1R)+ν_(2R)−ν_(3R)+ν_(4R), ν_(Rγ)=ν_(1R)−ν_(2R)+ν_(3R)−ν_(4R),and so on. Once again, it should be noted that in ν_(mat2), thesubscript X refers not to a variable color of light, but to theX-direction shown in FIGS. 3-5. In a different embodiment, the values ofν_(mat2) may differ by more than a factor of 4 while permitting a highlyaccurate determination of Δx, Δy, and γ.

Once Δx, Δy, and γ are determined, the deflection and twist of the shaft12 over the optical path 44 may be determined. In order to do so, fourreceiver output calibration parameters are required for each lightcolor: (a) the zero-deflection, zero-twist output of the receiverV_(det) _(_) _(i0); (b) the receiver output V_(det) _(_) _(i) _(_) _(α)_(_) _(cal) for a selected deflection α_(cal) in a first direction(i.e., along the X-axis in FIGS. 3-5); (c) the receiver output V_(det)_(_) _(i) _(_) _(β) _(_) _(cal) for a selected deflection β_(cal) in asecond direction (i.e., along the Y-axis in FIGS. 3-5); and (d) receiveroutput V_(det) _(_) _(i) _(_) _(γ) _(_) _(cal) for a selected twistγ_(cal). The resulting calibration matrix C_(mat), shown below as matrix(15), can be used according to equation (16), also shown below, to solveα, β, and γ given receiver output V_(det) _(_) _(i) for red, blue, andgreen light:

$\begin{matrix}{C_{mat} = \begin{bmatrix}\frac{V_{\det_{—}R_{—}\alpha_{—}{cal}} - V_{\det_{—}R\; 0}}{\alpha_{cal}} & \frac{V_{\det_{—}R_{—}\beta_{—}{cal}} - V_{\det_{—}R\; 0}}{\beta_{cal}} & \frac{V_{\det_{—}R_{—}\gamma_{—}{cal}} - V_{\det_{—}R\; 0}}{\gamma_{cal}} \\\frac{V_{\det_{—}B_{—}\alpha_{—}{cal}} - V_{\det_{—}B\; 0}}{\alpha_{cal}} & \frac{V_{\det_{—}B_{—}\beta_{—}{cal}} - V_{\det_{—}B\; 0}}{\beta_{cal}} & \frac{V_{\det_{—}B_{—}\gamma_{—}{cal}} - V_{\det_{—}B\; 0}}{\gamma_{cal}} \\\frac{V_{\det_{—}G_{—}\alpha_{—}{cal}} - V_{\det_{—}G\; 0}}{\alpha_{cal}} & \frac{V_{\det_{—}G_{—}\beta_{—}{cal}} - V_{\det_{—}G\; 0}}{\beta_{cal}} & \frac{V_{\det_{—}G_{—}\gamma_{—}{cal}} - V_{\det_{—}G\; 0}}{\gamma_{cal}}\end{bmatrix}} & (15) \\{\begin{pmatrix}\alpha \\\beta \\\gamma\end{pmatrix} = {{{inv}\left( C_{mat} \right)}\begin{pmatrix}{V_{\det_{—}R} - V_{\det_{—}R\; 0}} \\{V_{\det_{—}B} - V_{\det_{—}B\; 0}} \\{V_{\det_{—}G} - V_{\det_{—}G\; 0}}\end{pmatrix}}} & (16)\end{matrix}$

Once α, β, and γ have been solved, the external forces resulting indeflection and twisting of the shaft 12 can be calculated according tothe principles of elastostatics described above.

FIG. 6 is a schematic view of a system 50 for determining thedeformation (e.g., deflection, twisting, and/or other deformation) of adevice, such as catheter shaft 12, and corresponding forces applied tothe device. In an embodiment, the system 50 may include the force sensor26, including the light source 28, the optical filter 30, and theoptical receiver 32, disposed in or coupled to the catheter 10 and anelectronic control unit (ECU) 52. The ECU 52 may include a processor 54configured to execute instructions, code, or programming stored inmemory 56. The processor 54 may also be configured to store measurementsand calibration parameters in the memory 56, in an embodiment.

The memory 56 may include portions for storing values for use incalculating deformation of the catheter 10 (e.g., the distal end portion14 of the shaft 12 of the catheter 10), calculating the forces indicatedby deformation of the catheter 10, and/or other operations. In anembodiment, such portions may include a calibration values portion 58and a measured values portion 60. The processor may be configured towrite values to and read values from the calibration values and measuredvalues portions 58, 60 as described below.

The memory 56 may include light modulation instructions 62 for operatingor modulating the light source 28. Accordingly, the processor 54 mayexecute the light modulation instructions 62 to cause the light source28 to output light of different colors, frequencies, and/or frequencybands in a predetermined sequence, i.e., in a time-multiplexed fashion.A light sequence according to the light modulation instructions 62 mayinclude a number of time segments, with a single color, frequency, orfrequency band of light output during each time segment, such that thenumber of segments in the timing sequence is equal to the number ofcolors, frequencies, or frequency bands of light that the light source28 may output. Thus, in an embodiment, such a sequence may include thelight source 28 outputting red light for a first period of time, thenblue light for a second period of time, then green light for a thirdperiod of time, then red light again for the first period of time, andso on. The periods of time of each segment of the sequence may be equalto each other, in an embodiment. In another embodiment, the periods oftime of the segments of the sequence may be different from each other tofacilitate identification of time intervals when a specific color,frequency, and/or frequency band is produced.

The memory 56 may further include calibration instructions 64 forpopulating the calibration values portion 58 with appropriate values.Such population may involve calculating calibration parameters and/orretrieving calibration parameters from an external source and storingthose parameters to the calibration values portion 58. Accordingly, theprocessor 54 may execute the calibration instructions 64 to determineand/or receive calibration parameters. The calibration parameters mayinclude, but are not limited to, the calibration values discussed above,such as μ_(α), μ_(β), α_(cal), β_(cal), γ_(cal), V_(det) _(_) _(R) _(_)_(α) _(_) _(cal), V_(det) _(_) _(R) _(_) _(β) _(_) _(cal), and V_(det)_(_) _(R) _(_) _(γ) _(_) _(cal). In an embodiment, calibrationparameters may be calculated by the processor 54 by receiving one ormore signals from the optical receiver 32 during a calibration procedureas noted above. In the same or a different embodiment, calibrationparameters may be input by a user and received by the processor 54, orpre-stored and read by the processor 54 from the memory 56 or from someother data storage device (e.g., an EEPROM or other removable memorycoupled with the catheter 10).

The memory 56 may further include receiver output instructions 66 forreceiving and storing outputs from the optical receiver 32. Accordingly,the processor 54 may execute the receiver output instructions 66 toreceive a signal from the optical receiver 32 indicative of the amountof light detected by the receiver 32, process the signal to determinethe amount of light detected by the receiver 32, and associate thatlight amount with a particular color of light according to the output ofthe light source 28 known to the processor 54. The processor 54 may thenstore the light amount value or other data according to the signal inthe measured values portion 60 of the memory 56, determine deflection,twisting, or compression of the catheter as described below, or performsome alternative or additional operations with the signal or lightamount value.

The memory 56 may further include, and the processor 54 may beconfigured to execute, force calculation instructions 68 for calculatingone or more parameters of a deflection, twist, or other deformation of aportion of the catheter 10. For example, in an embodiment, the forcecalculation instructions 68 may include steps to construct and solve aseries of equations according to equations (4) and/or (15) above todetermine one or more deformation parameters or characteristics (e.g.,deflection angle α along a first axis, deflection angle β along a secondaxis, and twist angle γ about a third axis). Accordingly, the forcecalculation instructions 68 may include steps involving the use of thevalues stored in the calibration value measured value portions 56, 58for use in one or more equations. The force calculation instructions 68may further include steps to determine a force applied to the exteriorof the catheter 10 according to the determined deformation parameters.For example, in an embodiment, the force calculation instructions 68 mayinclude steps to construct and solve a series of equations according tothe linear elasticity equations (7)-(9) above.

The processor 54 may be configured, in an embodiment, to execute thecalibration instructions 64 at the beginning of a medical procedureusing the catheter 10. The processor 54 may be further configured toexecute the light modulation, receiver output, and force calculationinstructions 62, 66, 68 continuously throughout a medical procedure tomonitor the external forces applied to the catheter 10. If the processor54 detects a force or set of forces indicative of an undesirableposition, shape, or orientation of the catheter 10 relative to tissue(e.g., excess force indicating the possibility of tissue puncture), theECU 52 or other device may produce a visual, auditory, or other outputto inform the physician operating the catheter 10 of the undesirableposition, shape, or orientation. The ECU 52 may additionally oralternatively produce an output to indicate sufficient contact betweenthe catheter 10 (e.g., the distal tip 24) and tissue to perform aparticular procedure. For example, such a signal may be received by anablation system during an ablation procedure or a mapping system duringa mapping procedure.

Detecting external forces on the catheter 10 with the optical forcesensor 26 and the system 50 may be preferable to known devices, systems,and methods because of the relatively low complexity and cost of thesensor 26. Only a single light source 28 and a single receiver 32 may berequired, in an embodiment, to detect external forces with three or moredegrees-of-freedom; this contrasts with many known systems, which mayrequire a sensor per degree-of-freedom. Furthermore, the components ofthe sensor 26 may be very small in size, and thus may occupy littlespace within the catheter 10 and may maximize the amount of spaceavailable for other sensors, wiring, lumens, and other desirablefeatures.

The sensor 26 and/or system 50 may also find use in a remote catheterguidance system (RCGS) including, for example, robotic guidance andcontrol of one or more catheters. An exemplary system is described inU.S. patent application publication no. 2009/0247993, herebyincorporated by reference in its entirety as though fully set forthherein.

FIG. 7 is a diagrammatic view of an alternate embodiment of an opticalforce sensor 70. The force sensor 70 may be used instead of, or inaddition to, the force sensor 26 in the system 50 of FIG. 6 and in theother applications described herein. With continued reference to FIG. 7,the force sensor 70 may include a light source 72, a first polarizingfilter 74, a second polarizing filter 76, and an optical receiver 32.The light source 72 may be configured, in an embodiment, to providelight of a single frequency. The first polarizing filter 74 may berigidly coupled to the light source 72 to linearly polarize that lightin a first direction. The second polarizing filter 76 may be rigidlycoupled to the optical receiver 32 to polarize the light in a seconddirection that is offset by a selected amount from the first direction.In an embodiment, the second direction may be offset from the firstdirection by about forty-five degrees (45°).

In a neutral state, the optical receiver 32 may detect a first amount oflight. As the catheter 10 deforms, and the incident light 44 on thesecond filter 76 shifts or rotates, the optical receiver 32 may detect asecond amount of light. Depending on the relative shapes andorientations of the first and second filters 74, 76, the first amountdetected by the optical receiver 32 (in a neutral state) and the secondamount detected by the optical receiver 32 (in a non-neutral state) maybe different. For example, in the embodiment shown in FIG. 7, in whichthe second filter 76 is substantially the same shape and size as thefirst filter 74, but the polarization of the second filter 76 is offsetfrom the polarization of the first filter 74 by about forty-five degrees(45°), as the light source 72 rotates relative to the receiver 32, theamount of light detected by the receiver 32 will either increase (if therotation decreases the angular offset between the filters 74, 76) ordecrease (if the rotation increases the angular offset between thefilters 74, 76). Accordingly, the embodiment illustrated in FIG. 7 maybe particularly useful for detecting twist of the shaft 12. Otherarrangements of the filters 74, 76 may be used (e.g., multiple filtersegments with different polarizations in one or both of the filters 74,76, relative size or shape differences between the filters 74, 76, etc.)to better detect other deformations of the shaft 12.

FIG. 8 is a diagrammatic view of another alternate embodiment of anoptical force sensor 80, based on the same principles as the forcesensor 26 and system 50 illustrated and described above with respect toFIGS. 2-6. Accordingly, the sensor 80 may be used in addition to orinstead of the sensor 26 in the various systems and applicationsdescribed herein. With continued reference to FIG. 8, the sensor 80 mayinclude the light source 28, a first optical fiber 82, the filter 30, amirror 84, a second optical fiber 86, and the optical receiver 32. Thelight source 28, filter 30, and optical receiver 32 may functionsubstantially as described above with respect to the sensor 26.Furthermore, the sensor 80 may also be used in conjunction with thesystem 50, in addition to or instead of the sensor 26, in substantiallythe same manner described above in conjunction with FIG. 6 with respectto the system 50 and the sensor 26.

Referring again to FIG. 8, both the light source 28 and the receiver 32may be disposed outside the shaft 12, while the optical fibers 82, 86,the filter 30, and the mirror 84 may be disposed inside the shaft 12.More particularly, the filter 30 and mirror 84 may be disposed withinthe distal end portion 14 of the shaft 12. The first optical fiber 82may transmit a light beam generated by the light source 28 and projectthe beam along a first optical path 88 extending through the filter 30to the mirror 84, which may reflect the light along a second opticalpath 90 to the second optical fiber 86 for transmission to the opticalreceiver 32. In an embodiment, a lens (not shown) may be placed in thesecond optical path 90 to focus the light beam reflected by the mirror84 into the second optical fiber 86. Rather than measuring shaftdeformation between the light source 28 and the receiver 32, the sensormay be used to measure shaft deformation (and the accompanying forces onthe shaft 12) between the first optical fiber 82 and the filter 30.Because the light source 28 and receiver 32 may be located outside theshaft 12, in an embodiment, the sensor 80 may further reduce the spaceoccupied within the shaft 12 as compared to the sensor 26.

Although a number of embodiments of this invention have been describedabove with a certain degree of particularity, those skilled in the artcould make numerous alterations to the disclosed embodiments withoutdeparting from the spirit or scope of this invention. For example, alljoinder references (e.g., attached, coupled, connected, and the like)are to be construed broadly and may include intermediate members betweena connection of elements and relative movement between elements. Assuch, joinder references do not necessarily infer that two elements aredirectly connected and in fixed relation to each other. It is intendedthat all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative only and notlimiting. Changes in detail or structure may be made without departingfrom the spirit of the invention as defined in the appended claims.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialsdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as explicitly set forth hereinsupersedes any conflicting material incorporated herein by reference.Any material, or portion thereof, that is said to be incorporated byreference herein, but which conflicts with existing definitions,statements, or other disclosure material set forth herein will only beincorporated to the extent that no conflict arises between thatincorporated material and the existing disclosure material.

1.-20. (canceled)
 21. An apparatus for detecting deformation of anelongate body, the apparatus comprising: a light source configured toprovide light; an optical receiver configured to receive light from saidlight source; and a filter disposed between said light source and saidoptical detector, said filter comprising multiple segments, at least twoof said multiple segments configured to filter light at a differentfrequency so as to alter the amount of light incident on said opticalreceiver, wherein said optical receiver is configured to receive lightfrom all of the multiple segments of the filter; wherein a total amountof light received by said optical receiver is indicative of deformationof the elongate body.
 22. The apparatus of claim 21, wherein said lightsource is configured to provide light of multiple frequencies.
 23. Theapparatus of claim 22, wherein said light source is configured toprovide said light of multiple frequencies in a predetermined sequence.24. The apparatus of claim 22, wherein said filter comprises a firstnumber of segments, said light source is configured to provide light ofa second number of frequencies, and said first number is greater than orequal to said second number.
 25. The apparatus of claim 24, wherein saidfilter comprises at least four segments.
 26. The apparatus of claim 22,wherein light of all of said multiple frequencies is in the visiblespectrum.
 27. The apparatus of claim 22, wherein said light sourcecomprises a mechanically-single light source.
 28. The apparatus of claim27, wherein said light source comprises a multi-color LED.
 29. Theapparatus of claim 21, wherein the light source is configured to outputa non-circular projection on the filter.
 30. An elongate medical device,comprising: a handle; an elongate shaft having a proximal end portionand a distal end portion, said proximal end portion coupled with saidhandle, said elongate shaft configured for insertion into a body of apatient; a light source configured to provide light along an opticalpath, said optical path disposed at least in part within said distal endportion of said elongate shaft and contained completely within theelongate medical device; an optical receiver configured to receive lightprojected along said optical path; and a filter disposed in said opticalpath, said filter comprising multiple segments, at least two of saidmultiple segments configured to filter light at different frequencies soas to reduce the amount of light incident on said optical receiver. 31.The elongate medical device of claim 30, wherein said light source andsaid optical receiver are disposed in said distal end portion of saidshaft.
 32. The elongate medical device of claim 31, wherein said lightsource is disposed about 0.5 inches to about 2.0 inches from saidoptical receiver.
 33. The elongate medical device of claim 30, whereinsaid optical path is sealed from fluid.
 34. The elongate medical deviceof claim 30, wherein at least one of said light source and said opticalreceiver is disposed within about two inches of a distal tip of saidshaft.
 35. A system for assessing force on a medical device, the systemcomprising: an electronic control unit (ECU) configured to: couple to amedical device; operate a light source to emit light in a predeterminedsequence, said sequence comprising two or more time segments; receive asignal generated by an optical receiver responsive to said light outputby said light source; and process said signal in accordance with saidpredetermined sequence to determine an external force applied to themedical device and a magnitude and direction of a twisting of themedical device.
 36. The system of claim 35, wherein said ECU isconfigured to process said signal in accordance with said predeterminedsequence to determine a magnitude and a direction of a deflection of themedical device.
 37. The system of claim 35, wherein said ECU isconfigured to process said signal in accordance with said predeterminedsequence by determining an amount of light received by said opticaldetector at multiple different segments of said sequence.
 38. The systemof claim 35, wherein said light source is configured to provide light ofmultiple frequencies.
 39. The system of claim 35, wherein two of saidtime segments have different respective durations.
 40. The system ofclaim 35, wherein said ECU is configured to process said signal inaccordance with said predetermined sequence to determine a magnitude anda direction of said external force.